1. Field of the Invention
The present invention relates generally to a medical material, and particularly to an inorganic filler to be filled in defects or hollow portions formed by a removal operation of bone tumor or other causes in the bones of a living body to promote formation of new bone tissue at the filled portions and to coalesce with the bone tissue after the injured portions are completely cured.
2. Prior Art
In the surgical or orthopedic field, defects or hollow portions of bones are frequently formed by highly complicated fractures or a removal operation of bone tumor, and such defects or hollow portions should be cured by symphysis. In the prior art method, a cancellous bone is taken up from flank bones or other bones of the patient per se to be filled in the injured portion of bone to promote the cure of bone tissue. However, this prior art method is disadvantageous in that the patient suffers a greater pain from cumbersome labours necessitated in the operation, since a bone tissue other than the injured portion is taken out for use. Moreover, a sufficient amount of autoplastic bone cannot always be taken up from the patient's body for filling in a large defect or hollow portion of bone, and a certain substitute material is required to supplement the shortage of the required bone tissue in such a case.
Other than the method of autoplastic filling, there are a homogeneous bone implantation method and a heterogeneous bone implantation method. As to the homogeneous bone implantation method, uses of frozen bones and decalcified bones have been investigated but have not yet reached the stage of clinical practice. In the heterogeneous bone implantation method, a so-called keel bone, which is prepared by removing proteins from a bone of cattle, is used in some cases. However, both of these known methods are not only accompanied with foreign body reactions but also lack osteogenic capacity, so that the post-operation course is not always good. Accordingly, there is an increasing demand for an artificial filler material for filling in defects or hollow portions of bones which is excellent in compatibility with the living body and has high osteogenic capacity to promote the bone-forming reaction at the filled portion and at the vicinity thereof to accelerate curing of the structure and function of injured bone tissue.
With the aim to reducing the period of time required for curing the fractured bone, an internally fixing method is sometimes adopted wherein the fractured bone is directly fixed by the use of a metal plate, nail or screw. However, adopting such a method, there is often a case where so lengthy a time as six months or a whole year is necessary for complete curing. Furthermore, if the internally fixing method is adopted, the materials used for internal fixing should be removed from the patient's body after the fractured bone is cured, and thus the patient suffers tremendous physical, psychological and economical burdens. If a filler material of the aforementioned kind for promoting the osteogenic capacity and for accelerating the remedy or cure of the fractured or injured portion is developed, it will be made possible to attain the object of therapy for a short period of time without the application of the internally fixing method. The filler material of the aforementioned kind may be also used for the therapy of pseudoarthrosis. It is, therefore, considered that the development of such filler is of great medical value and contributes to welfare of humankind.
On the other hand, various metals and plastics materials have hitherto been used as the substitute materials for hard tissues of living body. However, these conventional materials are apt to be dissolved or deteriorated under the severe environment in the living body and are often accompanied with poisonous actions or foreign body reactions. For this reason, biomaterials of ceramics which have improved compatibilities with a living body attracted public attention in recent years. At the present time, an artificial bone, an artificial joint and an artificial radix dentis made of single crystalline or polycrystalline alumina (Al.sub.2 O.sub.3) and an artificial radix dentis made of sintered calcium tertiary phosphate (Ca.sub.3 (PO.sub.4).sub.2) or sintered hydroxyapatite (Ca.sub.5 (PO.sub.4).sub.3 OH) have been proposed. It has been reported that these materials are excellent in compatibility with a living body, for example, no appreciable formation of membrane caused by the foreign body reaction is observed when a sintered article of hydroxyapatite is implanted in a bone of a living body, which shows the direct connection between the sintered article and the bone tissue. However, these implantation materials are disadvantageously too hard and fragile, similarly as is the case of common ceramic materials, and should be improved in toughness and impact strength in order to use in the form of artificial bone or artificial radix dentis practically.